For some types of machined work pieces, it is desirable to have a non-circular profile (example: oval) where the positions of the major and minor diameters are precisely located on the work piece. For example, on pistons for internal combustion engines, such as in automobiles, lawnmowers, weed trimmers, leaf blowers, chainsaws, etc., it may be desirable to have the minor dimension substantially aligned with the wrist pin (the wrist pin rotatably connects the piston to the connecting rod). During, use, the piston may nonuniformly expand to a greater extent across the wrist pin dimension. By proper alignment of the major and minor diameters on the piston, this non-uniform expansion can be accounted for and the piston will take on a substantially circular shape upon reaching its equilibrium operating temperature. This results in better performance and may reduce noxious emissions.
Various machines are known for providing actively controlled machining. For example, in a paper entitled "Application Of An Actively Conti-oiled Magnetostrictive Actuator To Vibration Abatement In The Turning Process", ASME 1995 DSC-Vol. 57-1 IMECE, by T. J. Sturos et al. it was suggested that a magnetostrictive actuator, such as made from a Terfenol-D material, may be used in a lathe to impart active control forces to a vertically disposed flexibly mounted tool holder. A position sensor was used to implement feedback control of the tool position. It was indicated by the authors that a 40% improvement in surface roughness was achieved during cutting via reducing tool chatter phenomena. U.S. Pat. No. 4,646,595 to Slee describes a machine tool which includes an actively driven machine tool (see FIG. 4) for machining piston profiles. A frequency generator produces a very high frequency ultrasonic signal which is modulated by a modulator 11 and fed to an ultrasonic transducer 13. An axial sensor on the tool head provides feedback control of the tool. U.S. Pat. No. 5,085,109 to Hidehiko et al. teaches a system for machining non-circular work pieces having a second axis slider (3) which is slideably moved by a second axis servomotor (5) at high speed. However, in the Hidehiko et al. system, the slider (3) may undesirably tend to wear over time.
Another problem with machining non-circular profiles occurs when the frequency of the lathe changes during machining due to temperature changes, etc. During such events, it is desired to have an accurate input signal which is phase locked to the part rotation frequency.
Accordingly, there exists a need for a simple and cost effective method, apparatus and controller for providing high speed machining of non-circular work pieces. Furthermore, a need exists for a system where the generated output signal is insensitive to frequency changes.